Japanese Patent Application No. 58-44459 shows a printing device having a rotatable image-receiving support and a number of image-forming stations disposed along the rotational path of the image-receiving support. Each image-forming station uses a rotatable, cylindrical image-registration element and an imaging means to generate a separation image of a required image and to transfer the separation image to the image-receiving support in an image-transfer zone. In this particular printing device, there is an increasing distance, in each successive image-forming station, between each place where a separation image is formed on the image-registration element and the place where that separation image is transferred to the image-receiving support. The difference in the distances of two successive image-forming stations is equal to the distance between the image-transfer zones of the image-forming stations measured along the circumference of the image-receiving support. As a result of this arrangement, the start signal for forming the separation images can be given simultaneously for all the image-forming stations. A disadvantage of this device, however, is that its various parts, and particularly the image-registration elements and the image-receiving support, must be highly accurate to obtain the necessary registration requirements in the transfer of the separation images to the image-receiving support. A similar device is shown in the Abstract of Japanese Patent Application 61-65272 (Vol. 10, No. 232, Aug. 12, 1986) except that in this device the image-forming stations each contain a different color and are used to form a polychromatic image. This device has the disadvantages inherent with having different distances between the place where the separation image is formed and the place where it is transferred to the image-receiving element for each image-forming station.
Other multi-color printing devices are known. European Patent Application No. 163,791 shows a printing device having a central cylinder and a number of image-forming stations disposed along its rotational path. A paper sheet adheres to the central cylinder and a separation color image is transferred to the paper in each station. Similarly, U.S. Patent No. 3,392,667 discloses a multi-color offset printing machine having a number of plate cylinders disposed along the rotational path of a central offset cylinder for sequentially transferring colored powdered inks from the plate cylinders to the central offset cylinder.
U.K. Patent No. 1,277,233 describes a printing device which has only one image-forming station for forming the different separation images. The various separation images are produced in consecutive cycles and transferred successively to the image-receiving support. Although a highly accurate registration can be obtained with this device, it has the disadvantage that the separation images are formed consecutively so that the printing process is very time-consuming. Another disadvantage of this device is that it cannot print images which are longer than the circumference of the image-receiving support.
Other elements of a printing device are shown in the Abstract of Japanese Patent Application 60-209777 (Vol. 10, No. 72, Mar. 22, 1986); the Abstract of Japanese Patent Application 59-129888 (Vol. 8, No. 259, Nov. 28, 1984); and U.S. Patent No. 4,585,319. None of these references discloses a printing device having several image-forming stations disposed around a central image-receiving cylinder.
It would be desirable, therefore, to develop an improved printing device having a rotatable image-receiving support and a number of image-forming stations disposed around the image-receiving support which obviated the disadvantages mentioned above.